Method and apparatus for enhancing mobility for 3gpp lte-wlan aggregation in wireless communication system

ABSTRACT

As one aspect of mobility enhancement of 3rd generation partnership project (3GPP) long-term evolution (LTE)-wireless local area network (WLAN) aggregation, inter-eNodeB (eNB) handover without WLAN termination (WT) change is considered. A source eNB transmits a handover request message including a WT identifier (ID) and WT XwAP ID to a target eNB. The target eNB transmits a WT addition request message including the WT XwAP ID to a WT, and receives a WT addition request acknowledge message from the WT. The target eNB transmits a handover request acknowledge message indicating that a WT is kept to the source eNB. The source eNB transmits a WT release request message indicating that the WT is kept to the WT. The WT is a logical node that terminates a Xw interface on a WLAN.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119(e), this application claims the benefit ofU.S. Provisional Patent Application Nos. 62/317,416, filed on Apr. 1,2016 and 62/363,856, filed on Jul. 19, 2016, the contents of which areall hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for enhancing mobility for 3rdgeneration partnership project (3GPP) long-term evolution (LTE)-wirelesslocal area network (WLAN) aggregation in a wireless communicationsystem.

Related Art

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

With the ever increasing demand on mobile broadband services, the usageof unlicensed spectrum in general and wireless local area network (WLAN)in particular remains to be important for 3GPP operators. WLAN wasinitially deployed to provide opportunistic offload, however withincreasing demand for throughput efficient usage of unlicensed spectrum,operator control and reduced WLAN deployment costs become more and moreimportant.

In Rel-13, 3GPP defined LTE-WLAN aggregation (LWA) feature whichaddresses these requirements. Additionally, institute of electrical andelectronics engineers (IEEE) 802.11 specifications continue to evolve.IEEE 802.11 are working on 802.11ax which aims at increasing spectralefficiency in 2.4 and 5 GHz bands, in particular in dense deploymentswith a theoretical peak throughput up to 9.6 Gbps and 1.6 Gbps undermore realistic conditions. In the millimeter wave band of 60 GHz,802.11ad is a ratified amendment to 802.11 that defines a new physicallayer for 802.11 networks and can offer up to 7 Gbps throughputs.802.11ay is in the process of enhancing 802.11ad and aims at improvingmobility, range and providing data rates of at least 20 Gbps. Eventhough LWA framework has been designed largely agnostic to 802.11technologies, such increased data rates may require additionaloptimizations.

The enhanced LWA (eLWA) builds on Rel-13 LWA framework without changesto the LWA architecture and thus supports WLAN nodes deployed andcontrolled by operators and their partners. One of the objectives of theeLWA is mobility optimization.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for enhancingmobility for 3rd generation partnership project (3GPP) long-termevolution (LTE)-wireless local area network (WLAN) aggregation in awireless communication system. The present invention provides eNodeB(eNB)-triggered handover procedure without WLAN termination (WT) change.

In an aspect, a method for performing inter-eNodeB (eNB) handoverwithout wireless local area network (WLAN) termination (WT) change by asource eNB in a wireless communication system is provided. The methodincludes transmitting a handover request message including a WTidentifier (ID) and WT XwAP ID to a target eNB, receiving a handoverrequest acknowledge message indicating that a WT is kept from the targeteNB, and transmitting a WT release request message indicating that theWT is kept to the WT. The WT is a logical node that terminates a Xwinterface on a WLAN.

The WT ID may identify the WT.

The WT XwAP ID may be allocated by the WT and uniquely identify a userequipment (UE) over an Xw interface.

The handover request message may further include a mobility set of theWT.

The handover request message may further include information on E-UTRANradio access bearers (E-RABs) for the WT.

The handover request acknowledge message may further include a long-termevolution (LTE)-wireless local area network (WLAN) aggregation (LWA)configuration.

The handover request acknowledge message may further include a revisedmobility set for a UE based on selection of the target eNB.

The WT release request message may further include at least one of aneNB Xw AP ID, a WLAN Xw AP ID, or a cause to release.

In another aspect, a method for performing inter-eNodeB (eNB) handoverwithout wireless local area network (WLAN) termination (WT) change by atarget eNB in a wireless communication system is provided. The methodincludes receiving a handover request message including a WT identifier(ID) and WT XwAP ID from a source eNB, transmitting a WT additionrequest message including the WT XwAP ID to a WT, receiving a WTaddition request acknowledge message from the WT, and transmitting ahandover request acknowledge message indicating that the WT is kept tothe source eNB. The WT is a logical node that terminates an Xw interfaceon a WLAN.

The WT ID may identify the WT.

The WT XwAP ID may be allocated by the WT and uniquely identify a userequipment (UE) over an Xw interface.

The handover request message may further include a mobility set of theWT.

The WT addition request message may further include at least one of aneNB Xw AP ID, an E-UTRAN radio access bearer (E-RAB) ID, an E-RABquality of service (QoS), an eNB GPRS tunneling protocol (GTP) tunnelendpoint, a data forwarding indication, a security key, a selectedwireless local area network (WLAN) identifier or revised mobility set,or a WLAN media access control (MAC) address.

The handover request acknowledge message may further include a long-termevolution (LTE)-wireless local area network (WLAN) aggregation (LWA)configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows an overall architecture for the non-collocated LWAscenario.

FIG. 3 shows a method for performing inter-eNB handover without WTchange according to an embodiment of the present invention.

FIG. 4 shows a method for performing inter-eNB handover without WTchange by a source eNB according to an embodiment of the presentinvention.

FIG. 5 shows a method for performing inter-eNB handover without WTchange by a target eNB according to an embodiment of the presentinvention.

FIG. 6 shows a method for performing an eNB triggered WT changeaccording to an embodiment of the present invention.

FIG. 7 shows a method for performing an eNB triggered handover procedurewith WT release procedure according to an embodiment of the presentinvention.

FIG. 8 shows a method for performing an eNB triggered handover procedurewith direct WT addition procedure according to an embodiment of thepresent invention.

FIG. 9 shows a communication system to implement an embodiment of thepresent invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. Referring to FIG. 1, the LTEsystem architecture includes one or more user equipment (UE; 10), anevolved-UMTS terrestrial radio access network (E-UTRAN) and an evolvedpacket core (EPC). The UE 10 refers to a communication equipment carriedby a user. The UE 10 may be fixed or mobile, and may be referred to asanother terminology, such as a mobile station (MS), a user terminal(UT), a subscriber station (SS), a wireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), anaccess point, etc. One eNB 20 may be deployed per cell.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10. An uplink (UL) denotes communication from the UE 10 to theeNB 20. A sidelink (SL) denotes communication between the UEs 10. In theDL, a transmitter may be a part of the eNB 20, and a receiver may be apart of the UE 10. In the UL, the transmitter may be a part of the UE10, and the receiver may be a part of the eNB 20. In the SL, thetransmitter and receiver may be a part of the UE 10.

The EPC includes a mobility management entity (MME) and a servinggateway (S-GW). The MME/S-GW 30 provides an end point of session andmobility management function for the UE 10. For convenience, MME/S-GW 30will be referred to herein simply as a “gateway,” but it is understoodthat this entity includes both the MME and S-GW. A packet data network(PDN) gateway (P-GW) may be connected to an external network.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), packet data network (PDN)gateway (P-GW) and S-GW selection, MME selection for handovers with MMEchange, serving GPRS support node (SGSN) selection for handovers to 2Gor 3G 3GPP access networks, roaming, authentication, bearer managementfunctions including dedicated bearer establishment, support for publicwarning system (PWS) (which includes earthquake and tsunami warningsystem (ETWS) and commercial mobile alert system (CMAS)) messagetransmission. The S-GW host provides assorted functions includingper-user based packet filtering (by e.g., deep packet inspection),lawful interception, UE Internet protocol (IP) address allocation,transport level packet marking in the DL, UL and DL service levelcharging, gating and rate enforcement, DL rate enforcement based onaccess point name aggregate maximum bit rate (APN-AMBR).

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 is connected to the eNB 20 via a Uu interface. The UEs 10 areconnected to each other via a PC5 interface. The eNBs 20 are connectedto each other via an X2 interface. Neighboring eNBs may have a meshednetwork structure that has the X2 interface. The eNB 20 is connected tothe gateway 30 via an S1 interface.

LTE-wireless local area network (WLAN) aggregation (LWA) is described.It may be referred to Section 22A.1 of 3GPP TS 36.300 V13.2.0 (2015-12).E-UTRAN supports LWA operation whereby a UE in RRC_CONNECTED isconfigured by the eNB to utilize radio resources of LTE and WLAN. Twoscenarios are supported depending on the backhaul connection between LTEand WLAN, one of which is non-collocated LWA scenario for a non-idealbackhaul and the other is collocated LWA scenario for an ideal/internalbackhaul.

FIG. 2 shows an overall architecture for the non-collocated LWAscenario. Referring to FIG. 2, Referring to FIG. 7, in thenon-collocated LWA scenario, the eNB is connected to one or more WLANterminations (WTs) via an Xw interface. The WT terminates the Xwinterface, between the eNB and WT, for WLAN. The WT is a logical nodethat terminates the Xw interface on the WLAN side, and 3GPP may notspecify where it is implemented. In the collocated LWA scenario, theinterface between LTE and WLAN is up to implementation.

In LWA, the radio protocol architecture that a particular bearer usesdepends on the LWA backhaul scenario and how the bearer is set up. Twobearer types exist for LWA: split LWA bearer and switched LWA bearer.

For protocol data units (PDUs) sent over WLAN in LWA operation, the LWAadaptation protocol (LWAAP) entity generates LWA PDU containing a dataRB (DRB) identity and the WT uses the LWA EtherType for forwarding thedata to the UE over WLAN. The UE uses the LWA EtherType to determinethat the received PDU belongs to an LWA bearer and uses the DRB identityto determine to which LWA bearer the PDU belongs to. In the DL, LWAsupports split bearer operation where the packet data convergenceprotocol (PDCP) sublayer of the UE supports in-sequence delivery ofupper layer PDUs based on the reordering procedure introduced for dualconnectivity (DC). In the UL, PDCP PDUs can only be sent via the LTE.

The UE supporting LWA may be configured by the eNB to send PDCP statusreport or LWA PDCP status report, in cases where feedback from WT is notavailable.

For LWA, the only required interfaces to the Core Network are S1-U andS1-MME which are terminated at the eNB. No Core Network interface isrequired for the WLAN.

For user plane, in the non-collocated LWA scenario, the Xw user planeinterface (Xw-U) is defined between eNB and WT. The S1-U is terminatedat the eNB; the eNB and the WT are interconnected via Xw-U. The Xw-Uinterface supports flow control based on feedback from WT. The flowcontrol function is applied in the DL when an E-UTRAN radio accessbearer (E-RAB) is mapped onto an LWA bearer, i.e. the flow controlinformation is provided by the WT to the eNB for the eNB to control theDL user data flow to the WT for the LWA bearer. The Xw-U interface isused to deliver LWA PDUs between eNB and WT. For LWA, the S1-Uterminates in the eNB and, if Xw-U user data bearers are associated withE-RABs for which the LWA bearer option is configured, the user planedata is transferred from eNB to WT using the Xw-U interface.

For control plane, in the non-collocated LWA scenario, the Xw controlplane interface (Xw-C) is defined between eNB and WT. The S1-MME isterminated in eNB; the eNB and the WT are interconnected via Xw-C. Theapplication layer signaling protocol is referred to as Xw-AP (Xwapplication protocol). The Xw-AP protocol supports the followingfunctions:

-   -   Transfer of WLAN metrics (e.g. basic service set (BSS) load)        from WT to eNB;    -   Support of LWA for UE in evolved packet system (EPS) connection        management (ECM) connected state (ECM-CONNECTED): Establishment,        modification and release of a UE context at the WT, control of        user plane tunnels between eNB and WT for a specific UE for LWA        bearers.    -   General Xw management and error handling functions: Error        indication, setting up the Xw, resetting the Xw, updating the WT        configuration data.

eNB-WT control plane signaling for LWA is performed by means of Xw-Cinterface signaling. There is only one S1-MME connection per LWA UEbetween the eNB and the MME. Respective coordination between eNB and WTis performed by means of Xw interface signaling.

A WLAN mobility set is a set of one or more WLAN access points (APs)identified by one or more BSS identifier (BSSID)/home equivalent SSID(HESSID)/SSIDs, within which WLAN mobility mechanisms apply while the UEis configured with LWA bearer(s), i.e., the UE may perform mobilitybetween WLAN APs belonging to the mobility set without informing theeNB.

The eNB provides the UE with a WLAN mobility set. When the UE isconfigured with a WLAN mobility set, it will attempt to connect to aWLAN whose identifiers match the ones of the configured mobility set. UEmobility to WLAN APs not belonging to the UE mobility set is controlledby the eNB, e.g. updating the WLAN mobility set based on measurementreports provided by the UE. A UE is connected to at most one mobilityset at a time.

All APs belonging to a mobility set share a common WT which terminatesXw-C and Xw-U. The termination endpoints for Xw-C and Xw-U may differ.The WLAN identifiers belonging to a mobility set may be a subset of allWLAN identifiers associated to the WT.

The WT Addition procedure is initiated by the eNB and is used toestablish a UE context at the WT in order to provide WLAN resources tothe UE. The eNB decides to request the WT to allocate WLAN resources forspecific E-RABs, indicating E-RAB characteristics, by transmitting theWT Addition Request message. The WT may reject the request. If the WT isable to admit the full or partial WLAN resource request, it respondswith the WT Request Acknowledge message. The eNB sends theRRCConnectionReconfiguration message to the UE including the new radioresource configuration. The UE applies the new configuration and replieswith the RRCConnectionReconfigurationComplete message. The UE performsWLAN association. The WT sends the WT Association Confirmation message.If configured by the eNB, the UE may send the WLANConnectionStatusReportmessage.

The WT Release procedure may be initiated either by the eNB or by the WTand is used to initiate the release of the UE context at the WT. Therecipient node of this request cannot reject. It does not necessarilyneed to involve signaling towards the UE. In eNB initiated WT Release,the eNB requests the WT to release the allocated WLAN resources bytransmitting the WT Release Request message. The WT initiates release ofall allocated WLAN resources. If required, the eNB sends theRRCConnectionReconfiguration message to the UE indicating the release ofWLAN radio resource configuration. The UE replies with theRRCConnectionReconfigurationComplete message. The UE releases the LWAconfiguration towards the assigned WLAN resources. It is up to UEimplementation what happens with WLAN association after LWAconfiguration has been released.

Hereinafter, various enhanced mobility procedures for LWA are proposedaccording to embodiments of the present invention. According to theembodiments of the present invention, the enhanced mobility proceduresfor intra- and/or inter-eNB handover with/without WT change andimprovement of WT change are proposed.

1. First Embodiment: eNB Triggered Handover Procedure without WT Change

For this embodiment of the present invention, a use case that one WT hascoverage overlapping with two macro eNBs may exist. Thus, it is possiblethat the same WT is kept for a specific UE during the handover.Inter-eNB handover without WT change is used to transfer context datafrom a source eNB to a target eNB while the LWA connectivity is kept.

FIG. 3 shows a method for performing inter-eNB handover without WTchange according to an embodiment of the present invention.

In step S100, upon performing measurement of target eNB and/or WLAN, theUE may transmit measurement results of target eNB and/or WLAN to thesource eNB.

In step S110, the source eNB starts the handover procedure by initiatingthe X2 handover preparation procedure. That is, the source eNB transmitsthe Handover Request message to the target eNB. The source eNB mayinclude at least one of the followings in the Handover Request message.

a) Indication of keeping the WT: For example, it may be WT ID. WT ID ismay be used to identify the WT.

b) Selected WLAN identifier (e.g. SSID, BSSID, HESSID) or mobility set

c) Old WT XwAP ID: It may be WT UE XwAP ID which is allocated by the WTand uniquely identifies the UE over the Xw interface. It may let thetarget eNB and WT identify the UE.

d) Information on E-RABs for WLAN: E-RAB ID, quality of service (QoS),etc.

That is, the source eNB may include the LWA configuration in theHANDOVER REQUEST, and the LWA configuration may include the mobility setcurrently valid for the UE, the WT UE XwAP ID and WT ID as a referenceto the UE context in the WT that was established by the source eNB.

Table 1 shows an example of the Handover Request message according to anembodiment of the present invention.

TABLE 1 IE type and Semantics Assigned IE/Group Name Presence Rangereference description Criticality Criticality Message Type M 9.2.13 YESreject Old eNB UE X2AP M eNB UE Allocated at YES reject ID X2AP thesource ID eNB 9.2.24 Cause M 9.2.6 YES ignore Target Cell ID M ECGI YESreject 9.2.14 GUMMEI M 9.2.16 YES reject UE Context 1 YES rejectInformation >MME UE S1AP ID M INTEGER MME UE — — (0 . . . 2³² − S1APID 1) allocated at the MME >UE Security M 9.2.29 — — Capabilities >ASSecurity M 9.2.30 — — Information >UE Aggregate M 9.2.12 — — Maximum BitRate >Subscriber Profile O 9.2.25 — — ID for RAT/Frequencypriority >E-RABs To Be 1 — — Setup List >>E-RABs To Be 1 . . .<maxnoofBearers> EACH ignore Setup Item >>>E-RAB ID M 9.2.23 —— >>>E-RAB Level M 9.2.9 Includes — — QoS Parameters necessary QoSparameters >>>DL Forwarding O 9.2.5 — — >>>UL GTP Tunnel M GTP SGW — —Endpoint Tunnel endpoint of Endpoint the S1 9.2.1 transport bearer. Fordelivery of UL PDUs. >>>Bearer Type O 9.2.92 YES reject >RRC Context MOCTET Includes the — — STRING RRC Handover Preparation Informationmessage as defined in subclause 10.2.2 of TS 36.331 [9] >Handover O9.2.3 — — Restriction List >Location Reporting O 9.2.21 Includes the — —Information necessary parameters for location reporting >Management O9.2.59 YES ignore Based MDT Allowed >Management O MDT YES ignore BasedMDT PLMN PLMN List List 9.2.64 UE History M 9.2.38 Same YES ignoreInformation definition as in TS 36.413 [4] Trace Activation O 9.2.2 YESignore SRVCC Operation O 9.2.33 YES ignore Possible CSG Membership O9.2.52 YES reject Status Mobility O BIT Information YES ignoreInformation STRING related to the (SIZE handover; the (32)) source eNBprovides it in order to enable later analysis of the conditions that ledto a wrong HO. Masked IMEISV O 9.2.69 YES ignore UE History O OCTETVisitedCellInfo YES ignore Information from the STRING List UE containedin the UEInformation Response message (TS 36.331 [9]) Expected UE O9.2.70 YES ignore Behaviour ProSe Authorized O 9.2.78 YES ignore UEContext O YES ignore Reference at the SeNB >Global SeNB ID M Global eNBID 9.2.22 >SeNB UE X2AP M eNB UE Allocated at ID X2AP the SeNB ID9.2.24 >SeNB UE X2AP O Extended Allocated at ID Extension eNB the SeNBUE X2AP ID 9.2.86 Old eNB UE X2AP O Extended Allocated at YES reject IDExtension eNB the source UE eNB X2AP ID 9.2.86 V2X Services O 9.2.93 YESignore Authorized UE Context O YES ignore Reference at the WT >WT ID M9.2.x >WT UE XwAP ID M 9.2.y

Referring to Table 1, the Handover Request message may include the “UEContext Reference at the WT” information element (IE) according to anembodiment of the present invention. The “UE Context Reference at theWT” IE may include the “WT ID” IE and/or “WT UE XwAP ID” IE, accordingto an embodiment of the present invention.

The “WT ID” IE corresponds to a) the indication of keeping the WT, i.e.WT ID, in step S110. Table 2 shows an example of the “WT ID” IEaccording to an embodiment of the present invention.

TABLE 2 IE type and Semantics IE/Group Name Presence Range referencedescription CHOICE WT ID M Type >WT ID Type 1 >>PLMN ID M PLMN Identity9.2.4 >>Short WT ID M BIT STRING (24) >WT ID Type 2 >>Long WT ID M BITSTRING (48)

The “WT UE XwAP ID” IE corresponds to c) the old WT XwAP ID, in stepS110. Table 3 shows an example of the “WT UE XwAP ID” IE according to anembodiment of the present invention.

TABLE 3 IE type and Semantics IE/Group Name Presence Range referencedescription WT UE XwAP M OCTET STRING ID (SIZE(3))

If the target eNB decides to keep the WT, in step S120, the target eNBtransmits the WT Addition Request message to the WT. The WT AdditionRequest message may include at least one of the followings:

a) eNB Xw AP ID to identify the UE

b) E-RAB ID, E-RAB QoS, eNB GPRS tunneling protocol (GTP) tunnelendpoint (for UL PDU delivery)

c) Data forwarding indication

d) Security key

e) Selected WLAN identifier (e.g. SSID, BSSID, HESSID) or revisedmobility set

f) Old WT XwAP ID to let the WT identify the UE

g) WLAN media access control (MAC) address

That Is, if the target eNB decides to keep the LWA connection, thetarget eNB transmits the WT Addition Request message to the WT includingthe WT UE XwAP ID as a reference to the UE context in the WT that wasestablished by the source eNB. All or a part of the informationdescribed above may be received from the source eNB in step S110.

Table 4 shows an example of the WT Addition Request message according toan embodiment of the present invention.

TABLE 4 IE type and Semantics Assigned IE/Group Name Presence Rangereference description Criticality Criticality Message Type M 9.2.1 YESreject eNB UE XwAP ID M UE Assigned by YES reject XwAP the eNB ID 9.2.24UE Identity M 9.2.16 YES reject WLAN Security O 9.2.27 YES rejectInformation Serving PLMN O PLMN The serving YES ignore Identity PLMN forthe 9.2.3 UE. E-RABs To Be 1 YES reject Added List >E-RABs To Be 1 . . .<maxnoofBearers> EACH reject Added Item >>E-RAB ID M 9.2.18 — — >>E-RABLevel M 9.2.19 Includes — — QoS Parameters necessary QoS parameters >>eNB GTP Tunnel M GTP Endpoint of — — Endpoint Tunnel the Xw Endpointtransport 9.2.22 bearer at the eNB Mobility Set M 9.2.28 YES reject WTUE XwAP ID O UE Previously YES reject XwAP assigned by ID the WT 9.2.24

Referring to Table 4, the WT Addition Request message may include the“WT UE XwAP ID” IE according to an embodiment of the present invention.The “WT UE XwAP ID” IE corresponds to f) the old WT XwAP ID, in stepS120. The “WT UE XwAP ID” IE uniquely identifies a UE over the Xwinterface within a WT or an eNB.

The WT shall use the information in the WT Addition Request message tocheck if the UE context is present. If successful, in step S130, the WTreplies with the WT Addition Request Acknowledge message to the targeteNB. The WT Addition Request Acknowledge message may include at leastone of the followings:

a) eNB Xw AP ID, WLAN Xw AP ID to identify the UE

b) Admitted E-RAB IDs, WLAN GTP tunnel endpoint (for DL PDU delivery)

c) Not admitted E-RAB IDs

d) Data forwarding tunnel endpoint IDs (TEIDs)

e) Indication of whether WLAN is kept or not

If the target eNB and the WT have decided to keep the UE context in theWT in step S120 and S130, in step S140, the target eNB transmits theHandover Request Acknowledge message to the source eNB by including atleast one of the followings.

a) Indication of whether WLAN is kept or not

b) Revised mobility set for UE based on target eNB's selection

c) LWA configuration in RRC container to configure UE: LWA bearer addedor removed

That is, if both the target eNB and the WT decided to keep the LWAconnection in steps S120 and S130 respectively, the target eNB transmitsthe Handover Request Acknowledge message, which includes the LWAconfiguration and the UE LWA context kept indicator. The HandoverRequest Acknowledge message may also provide forwarding addresses to thesource eNB.

Table 5 shows an example of the Handover Request Acknowledge messageaccording to an embodiment of the present invention.

TABLE 5 IE type and Semantics Assigned IE/Group Name Presence Rangereference description Criticality Criticality Message Type M 9.2.13 YESreject Old eNB UE X2AP M eNB UE Allocated YES ignore ID X2AP at the IDsource 9.2.24 eNB New eNB UE X2AP M eNB UE Allocated YES ignore ID X2APat the ID target 9.2.24 eNB E-RABs Admitted 1 YES ignore List > E-RABsAdmitted 1 . . . <maxnoofBearers> EACH ignore Item >>E-RAB ID M 9.2.23 —— >>UL GTP Tunnel O GTP Identifies — — Endpoint Tunnel the X2 Endpointtransport 9.2.1 bearer used for forwarding of UL PDUs >>DL GTP Tunnel OGTP Identifies — — Endpoint Tunnel the X2 Endpoint transport 9.2.1bearer. used for forwarding of DL PDUs E-RABs Not O E-RAB A value YESignore Admitted List List for E- 9.2.28 RAB ID shall only be presentonce in E-RABs Admitted List IE and in E- RABs Not Admitted List IE.Target eNB To M OCTET Includes YES ignore Source eNB STRING the RRCTransparent E-UTRA Container Handover Command message as defined insubclause 10.2.2 in TS 36.331 [9] Criticality O 9.2.7 YES ignoreDiagnostics UE Context Kept O 9.2.85 YES ignore Indicator Old eNB UEX2AP O Extended Allocated YES ignore ID Extension eNB UE at the X2APsource ID eNB 9.2.86 New eNB UE X2AP O Extended Allocated YES reject IDExtension eNB UE at the X2AP target ID eNB 9.2.86 WT UE Context O UEIndicates YES ignore Kept Indicator Context that Kept the WT Indicatorhas 9.2.85 acknowledged to keep the UE context

Referring to Table 5, the Handover Request Acknowledge message mayinclude the “WT UE Context Kept Indicator” IE according to an embodimentof the present invention. The “WT UE Context Kept Indicator” IEcorresponds to a) the indication of whether WLAN is kept or not, in stepS140.

In step S150, the source eNB transmits the WT Release Request message tothe WT. The source eNB indicates to the WT that the UE context in the WTis kept. If the indication as the UE context kept in WT is included, theWT keeps the UE context. The WT Release Request message may include atleast one of the followings.

a) eNB Xw AP ID, WLAN Xw AP ID to identify the UE

b) Cause to release

c) Indication of whether WLAN is kept or not

That is, the source eNB transmits the WT Release Request message to theWT, indicating whether the UE context has been matched at the targeteNB. The WT keeps the relevant part of the UE context based on theidentification information provided from the target eNB at step S120.

Table 6 shows an example of the WT Release Request message according toan embodiment of the present invention.

TABLE 6 IE type and Semantics Assigned IE/Group Name Presence Rangereference description Criticality Criticality Message Type M 9.2.1 YESignore eNB UE XwAP ID M UE Assigned YES reject XwAP by the ID eNB 9.2.24WT UE XwAP ID M UE Assigned YES reject XwAP by the ID WT 9.2.24 Cause O9.2.4 YES ignore E-RABs To Be 0 . . . 1 YES ignore Released List >E-RABsTo Be 1 . . . <maxnoofBearers> EACH ignore Released Item >>E-RAB ID M9.2.18 — — >>DL Forwarding O GTP Identifies — — GTP Tunnel Tunnel the XwEndpoint Endpoint transport 9.2.22 bearer. used for forwarding of DLPDUs UE Context Kept O 9.2.x YES ignore Indicator

Referring to Table 6, the WT Release Request message may include the “UEContext Kept Indicator” IE according to an embodiment of the presentinvention. The “UE Context Kept Indicator” IE corresponds to c) theindication of whether WLAN is kept or not, in step S150. Table 7 showsan example of the “UE Context Kept Indicator” IE according to anembodiment of the present invention. This IE indicates that the UEcontext at the WT is kept in case of inter-eNB handover without WTchange procedure.

TABLE 7 IE type and Semantics IE/Group Name Presence Range referencedescription UE Context M ENUMERATED Kept Indicator (True, . . .)

Upon reception of the WT Release Request message containing the “UEContext Kept Indicator” IE set to “True”, the WT shall, if supported,only initiate the release of the resources related to the UE-associatedsignaling connection between the eNB and the WT. Further, the source eNBmay postpone sending the WT Release Request message until the UE ContextRelease message, which will be described below, is received.

In step S160, the source eNB triggers the UE to apply the newconfiguration.

In step S170, the UE synchronizes to the target eNB and replies with theRRCConnectionReconfigurationComplete message, which is also sent to theWT to notify configuration complete in step S171. The order of stepsS150 and S160/S170/S171 can be adjusted.

In step S180, the UE accesses to the WT.

In step S190, the WT transmits the WT Association Confirmation messageto the target eNB if the UE accesses the WLAN successfully, whichnotifies it to the WT. The WT Association Confirmation message mayinclude eNB Xw AP ID, WLAN Xw AP ID to identify the UE.

In step S200, the UE may also notifies the target eNB of the status ofaccess to the WLAN by transmitting the WLAN Connection Status Reportmessage.

In step S210/S220, the target eNB initiates the S1 path switch proceduretowards the MME.

In step S230, the target eNB initiates the UE Context Release proceduretowards the source eNB.

In step S240, upon reception of the UE Context Release message, the WTcan release C-plane related resource associated to the UE contexttowards the source eNB. Any ongoing data forwarding may continue. The WTshall not release the UE context associated with the target eNB if theindication was included in the WT Release Request message in step S150.

Sometime after the handover without WT change procedure, the target eNBmay provide the UE and the WT with new WLAN security information. Basedon this information, the UE re-authenticates itself in the WLAN.

Before the source eNB initiates the WT Release Request procedure, the WTis configured with bearer tunnels to both the source and target eNB.According to the inter-eNB handover procedure without WT changeaccording to an embodiment of the present invention, in the DL, thesource eNB forwards end marker packets immediately after the last datapackets sent to the WT for a particular bearer, and the WT forwardspackets received from either eNB towards the UE. The end marker packetsmay be used by the UE to switch the PDCP key. In the UL, the UE insertsend marker packets to indicate the key switch. The source eNB may usethe end marker packets to infer which packets it should process ordiscard while the source Xw-u tunnel is operational. The target eNBprocesses all received packets.

FIG. 4 shows a method for performing inter-eNB handover without WTchange by a source eNB according to an embodiment of the presentinvention.

In step S300, the source eNB transmits a handover request messageincluding a WT ID and WT XwAP ID to a target eNB. The WT ID may identifythe WT. The WT XwAP ID may be allocated by the WT and may uniquelyidentify a UE over an Xw interface. The handover request message mayfurther include a mobility set of the WT. The handover request messagefurther includes information on E-RABs for the WT.

In step S310, the source eNB receives a handover request acknowledgemessage indicating that a WT is kept from the target eNB. The handoverrequest acknowledge message may further include a LWA configuration. Thehandover request acknowledge message may further include a revisedmobility set for a UE based on selection of the target eNB.

In step S320, the source eNB transmits a WT release request messageindicating that the WT is kept to the WT. The WT release request messagemay further include at least one of an eNB Xw AP ID, a WLAN Xw AP ID, ora cause to release.

FIG. 5 shows a method for performing inter-eNB handover without WTchange by a target eNB according to an embodiment of the presentinvention.

In step S400, the target eNB receives a handover request messageincluding a WT ID and WT XwAP ID from a source eNB. The WT ID mayidentify the WT. The WT XwAP ID may be allocated by the WT and mayuniquely identify a UE over an Xw interface. The handover requestmessage may further include a mobility set of the WT.

In step S410, the target eNB transmits a WT addition request messageincluding the WT XwAP ID to a WT. The WT addition request message mayfurther include at least one of an eNB Xw AP ID, an E-RAB ID, an E-RABQoS, an eNB GTP tunnel endpoint, a data forwarding indication, asecurity key, a selected WLAN identifier or revised mobility set, or aWLAN MAC address.

In step S420, the target eNB receives ng a WT addition requestacknowledge message from the WT.

In step S430, the target eNB transmits a handover request acknowledgemessage indicating that the WT is kept to the source eNB. The handoverrequest acknowledge message may further include a LWA configuration.

2. Second Embodiment: eNB Triggered WT Change Procedure

In the coverage area of the eNB, there may be several WTs. Accordingly,the change of WT for a specific UE may occur.

FIG. 6 shows a method for performing an eNB triggered WT changeaccording to an embodiment of the present invention.

In step S500, upon performing measurement of WLAN, the UE may transmitmeasurement results of or WLAN to the eNB.

In step S510, the eNB transmits the WT Addition Request message to theWT2. The WT Addition Request message may include at least one of thefollowings:

a) eNB Xw AP ID to identify the UE

b) E-RAB ID, E-RAB QoS, eNB GTP tunnel endpoint (for UL PDU delivery)

c) Data forwarding indication

d) Security key

e) selected WLAN identifier (e.g. SSID, BSSID, HESSID)

In step S520, the WT2 transmits the WT Addition Request Acknowledgemessage to the eNB. The WT Addition Request Acknowledge message mayinclude at least one of the followings:

a) eNB Xw AP ID, WLAN Xw AP ID to identify the UE

b) Admitted E-RAB IDs, WLAN GTP tunnel endpoint (for DL PDU delivery)

c) Not admitted E-RAB IDs

d) Data forwarding TEIDs

In step S530, the eNB transmits the WT Release Request message to theWT1. The WT Release Request message may include at least one of thefollowings.

a) eNB Xw AP ID, WLAN Xw AP ID to identify the UE

b) E-RAB to be released: E-RAB ID, DL/UL forwarding GP tunnel endpoint

c) Cause to release

In step S540, the eNB triggers the UE to apply the new configuration. Instep S550, the UE transmits the RRCConnectionReconfigurationCompletemessage to the eNB.

In step S560, the eNB transmits the WT Reconfiguration Complete messageto the WT2. The WT Reconfiguration Complete message may include eNB XwAP ID, WLAN Xw AP ID to identify the UE.

In step S570, the WT2 transmits the WT Association Confirmation messageto the eNB. The WT Association Confirmation message may include eNB XwAP ID, WLAN Xw

AP ID to identify the UE.

3. Third Embodiment: eNB Triggered Handover Procedure with WT ReleaseProcedure Together

For this embodiment of the present invention, a use case that one WT hascoverage overlapping with two Macro eNBs may exist. Thus, it is possiblethat the original WT is released for a specific UE during the handover.

FIG. 7 shows a method for performing an eNB triggered handover procedurewith WT release procedure according to an embodiment of the presentinvention.

In step S600, upon performing measurement of WLAN, the UE may transmitmeasurement results of or WLAN to the source eNB.

In step S610, the source eNB transmits the Handover Request message withadditional indication on potential WT available to the target eNB. TheHandover Request message may further includes a selected WLAN identifier(e.g. SSID, BSSID, HESSID).

In step S620, the target eNB transmits the Handover Request Acknowledgemessage to the source eNB.

In step S630, the source eNB transmits the WT Release Request message tothe WT. The WT Release Request message may include at least one of thefollowings.

a) eNB Xw AP ID, WLAN Xw AP ID to identify the UE

b) E-RAB to be released: E-RAB ID, DL/UL forwarding GP tunnel endpoint

c) Cause to release

In step S640, the source eNB triggers the UE to apply the newconfiguration.

In step S650, the UE synchronizes to the target eNB and replies with theRRCConnectionReconfigurationComplete message.

In step S660, the target eNB initiates the UE Context Release proceduretowards the source eNB.

4. Fourth Embodiment: eNB Triggered Handover Procedure with Direct WTAddition Procedure Together

For this embodiment of the present invention, a use case that one WT hascoverage overlapping with two Macro eNBs may exist. Thus, it is possiblethat the target eNB may trigger the WT addition directly for a specificUE during the handover.

FIG. 8 shows a method for performing an eNB triggered handover procedurewith direct WT addition procedure according to an embodiment of thepresent invention.

In step S700, upon performing measurement of WLAN, the UE may transmitmeasurement results of or WLAN to the source eNB.

In step S710, the source eNB transmits the Handover Request message,with WLAN measurement results to assist the target eNB for a decision,to the target eNB.

In step S720, the target eNB transmits the WT Addition Request messageto the target WT. The WT Addition Request message may include at leastone of the followings:

a) eNB Xw AP ID to identify the UE

b) E-RAB ID, E-RAB QoS, eNB GTP tunnel endpoint (for UL PDU delivery)

c) Data forwarding indication

d) Security key

e) selected WLAN identifier (e.g. SSID, BSSID, HESSID)

In step S730, the target WT transmits the WT Addition RequestAcknowledge message to the target eNB. The WT Addition RequestAcknowledge message may include at least one of the followings:

a) eNB Xw AP ID, WLAN Xw AP ID to identify the UE

b) Admitted E-RAB IDs, WLAN GTP tunnel endpoint (for DL PDU delivery)

c) Not admitted E-RAB IDs

d) Data forwarding TEIDs

In step S740, the target eNB transmits the Handover Request Acknowledgemessage to the source eNB.

In step S750, the source eNB triggers the UE to apply the newconfiguration.

In step S760, the UE synchronizes to the target eNB and replies with theRRCConnectionReconfigurationComplete message, which is also sent to thetarget WT to notify configuration complete in step S770.

In step S780, the target WT transmits the WT Association Confirmationmessage to the target eNB. The WT Association Confirmation message mayinclude eNB Xw AP ID, WLAN Xw AP ID to identify the UE.

In step S790, the target eNB initiates the UE Context Release proceduretowards the source eNB.

FIG. 9 shows a communication system to implement an embodiment of thepresent invention.

A source eNB 800 includes a processor 810, a memory 820 and atransceiver 830. The processor 810 may be configured to implementproposed functions, procedures and/or methods described in thisdescription. Layers of the radio interface protocol may be implementedin the processor 810. The memory 820 is operatively coupled with theprocessor 810 and stores a variety of information to operate theprocessor 810. The transceiver 830 is operatively coupled with theprocessor 810, and transmits and/or receives a radio signal.

A target eNB 900 includes a processor 910, a memory 920 and atransceiver 930. The processor 910 may be configured to implementproposed functions, procedures and/or methods described in thisdescription. Layers of the radio interface protocol may be implementedin the processor 910. The memory 920 is operatively coupled with theprocessor 910 and stores a variety of information to operate theprocessor 910. The transceiver 930 is operatively coupled with theprocessor 910, and transmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The transceivers 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

According to the present invention, mobility for LWA can be enhanced.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What is claimed is:
 1. A method for performing an inter-base stationhandover by a source base station when a cellular network and a wirelesslocal area network (WLAN) are aggregated, the inter-base stationhandover for a user equipment (UE) currently connected to both thesource base station and a WLAN termination (WT) so that the UE is handedover to a target base station from the source base station withoutchanging the WT, the method comprising: transmitting, to the target basestation, a handover request message including a WT identifier (ID) andWT XwAP ID; receiving, from the target base station, a handover requestacknowledge message informing that the WT is kept; and transmitting, tothe WT, a WT release request message informing that the WT is kept,wherein the WT is a logical node that terminates a Xw interface on theWLAN, wherein the Xw interface is an interface established between theWT and the source base station, and between the WT and the target basestation, wherein the WT ID identifies the WT, wherein the WT XwAP ID isallocated by the WT and uniquely identifies the UE over the Xwinterface, wherein the handover request message further includes amobility set of the WT, wherein the mobility set is a set of one or moreWLAN access points (APs) identified by one or more of a BSS identifier(BSSID), a home equivalent SSID (HESSID) and an SSID.
 2. The method ofclaim 1, wherein the handover request message further includesinformation on E-UTRAN radio access bearers (E-RABs) for the WT.
 3. Themethod of claim 1, wherein the handover request acknowledge messagefurther includes a revised mobility set for the UE based on selection ofthe target base station.
 4. The method of claim 1, wherein the WTrelease request message further includes at least one of an eNodeB (eNB)Xw AP ID, a WLAN Xw AP ID, or a cause to release.
 5. A method forperforming an inter-base station handover by a target base station whena cellular network and a wireless local area network (WLAN) areaggregated, the inter-base station handover for a user equipment (UE)currently connected to both a source base station and a WLAN termination(WT) so that the UE is handed over to the target base station from thesource base station without changing the WT, the method comprising:receiving, from the source base station, a handover request messageincluding a WT identifier (ID) and WT XwAP ID; transmitting, to a WT, aWT addition request message including the WT XwAP ID; receiving, fromthe WT, a WT addition request acknowledge message; and transmitting, tothe source base station, a handover request acknowledge messageinforming that the WT is kept, wherein the WT is a logical node thatterminates a Xw interface on a WLAN, wherein the Xw interface is aninterface established between the WT and the source base station, andbetween the WT and the target base station, wherein the WT ID identifiesthe WT, wherein the WT XwAP ID is allocated by the WT and uniquelyidentifies the UE over the Xw interface, wherein the handover requestmessage further includes a mobility set of the WT, wherein the mobilityset is a set of one or more WLAN access points (APs) identified by oneor more of a BSS identifier (BSSID), a home equivalent SSID (HESSID) andan SSID.
 6. The method of claim 5, wherein the WT addition requestmessage further includes at least one of an eNodeB (eNB) Xw AP ID, anE-UTRAN radio access bearer (E-RAB) ID, an E-RAB quality of service(QoS), an eNB GPRS tunneling protocol (GTP) tunnel endpoint, a dataforwarding indication, a security key, a selected WLAN identifier orrevised mobility set, or a WLAN media access control (MAC) address.